1. Field of the Invention
The invention relates to blood pressure monitoring apparatuses to be applied to such fields as requiring continuous blood pressure monitoring for subjects to be treated in operating rooms, intensive care units, emergency treatment rooms, artificial dialysis treatment rooms, and the like. More particularly, the invention is directed to a blood pressure monitoring apparatus that monitors blood pressure by means of pulse wave propagation time.
2. Related Art
Known as a blood pressure monitoring apparatus that monitors blood pressure by continuously measuring the blood pressure of a subject are a noninvasive blood pressure measurement type based on an oscillometric method by wrapping a cuff around the brachium of a subject and an invasive blood pressure measurement type that involves insertion of an instrument into the aorta of the subject.
By the way, a conventional blood pressure monitoring apparatus has addressed the following problems.
(1) In a blood pressure monitoring apparatus that measures blood pressure in a noninvasive manner using a cuff, the problem arises when blood pressure is measured regularly at a long time interval. That is, a sudden turn for the worse such as a shock in blood pressure has, in some cases, been missed when the blood pressure is measured at a time interval exceeding 5 minutes, for example. It may be noted that by shortening the measuring cycle to, e.g., 1 minute, the likelihood of missing sudden changes in blood pressure can be reduced. However, when the measuring cycle is shortened, burden is given to the blood vessel of a body part around which the cuff is wrapped. PA0 (2) Further, when blood pressure is measured regularly, the subject is burdened with the part of his or her body being pressured with the cuff more frequently than necessary. PA0 (3) In a blood pressure monitoring apparatus of the invasive measurement type, the subject may, in some cases, be spiritually burdened by stress. Further, such blood pressure monitoring apparatus entails more cumbersome operation than a blood pressure monitoring apparatus of the noninvasive blood pressure measurement type, which in turn burdens the medical staff as well.
Therefore, the object of the invention is to provide a blood pressure monitoring apparatus that can monitor blood pressure continuously, safely, and highly accurately without giving burden to a subject.
According to an aspect of the present invention, there is provided a blood pressure monitoring apparatus including a blood pressure measuring means for measuring blood pressure using a cuff; a storage means for storing a pulse wave propagation time change threshold and a cardiovascular dynamic change threshold, both thresholds being inputted from an external means; a time interval detection reference point detecting means for detecting a time interval detection reference point on a pulse wave at an aorta of a body; a pulse wave detecting means for detecting a pulse wave at a peripheral blood vessel appearing with a time delay with respect to the pulse wave at the aorta; a pulse wave propagation time counting means for counting a pulse wave propagation time based on detected outputs from the time interval detection reference point detecting means and the pulse wave detecting means; a pulse wave propagation time change calculating means for calculating a pulse wave propagation time change from the two pulse wave propagation times counted by the pulse wave propagation time counting means; a cardiovascular dynamic change calculating means for calculating a cardiovascular dynamic change from the time interval detection reference point or the pulse wave at the peripheral blood pressure; a first judging means for judging whether or not the pulse wave propagation time change calculated by the pulse wave propagation time change calculating means exceeds the pulse wave propagation time change threshold stored in the storage means; a second judging means for judging whether or not the cardiovascular dynamic change calculated by the cardiovascular dynamic change calculating means exceeds the cardiovascular dynamic change threshold stored in the storage means; and a control means for controlling the blood pressure measuring means and for measuring blood pressure of a subject using the cuff if it is judged that the pulse wave propagation time change exceeds the pulse wave propagation time change threshold or if it is judged that the cardiovascular dynamic change exceeds the cardiovascular dynamic change threshold.
The present invention is provided as using a value equivalent to a heart rate change as a cardiovascular dynamic change threshold, causing the cardiovascular dynamic change calculating means to calculate a heart rate change based on the time interval detection reference point, and by causing the second judging means to judge whether or not the heart rate change exceeds the cardiovascular dynamic change threshold equivalent to the heart rate change.
The present invention is provided as using a value equivalent a rate of change of an amplitude of a pulse wave of a peripheral blood vessel as a cardiovascular dynamic change threshold, and causing the cardiovascular dynamic change calculating means to calculate the rate of change of the amplitude of the pulse wave of the peripheral blood vessel based on the pulse wave at the peripheral blood vessel, and causing the second judging means to judge whether or not the rate of change of the amplitude of the pulse wave exceeds the cardiovascular dynamic change threshold equivalent to the rate of change of the amplitude of the pulse wave of the peripheral blood vessel.
The present invention is provided as using a value equivalent to a rate of change of a dc component of a pulse wave of a peripheral blood vessel as a cardiovascular dynamic change threshold, causing the cardiovascular dynamic change calculating means to calculate the rate of change of the dc component of the pulse wave based on the pulse wave at the peripheral blood vessel, and causing the second judging means to judge whether or not the rate of change of the dc component of the pulse wave exceeds the cardiovascular dynamic change threshold equivalent to the rate of change of the dc component of the pulse wave of the peripheral blood vessel.
The present invention is provided as using a heart rate change, a rate of change of an amplitude of a pulse wave of a peripheral blood vessel, and a rate of change of a dc component of a pulse wave of a peripheral blood vessel as cardiovascular dynamic change thresholds; causing the cardiovascular dynamic change calculating means to calculate not only the heart rate change based on the time interval detection reference point, but also the rate of change of the amplitude of the pulse wave and the rate of change of the dc component of the pulse wave based on the pulse wave at the peripheral blood vessel; causing the second judging means to judge whether or not the heart rate change exceeds the cardiovascular dynamic change threshold equivalent to the heart rate change, whether or not the rate of change of the amplitude of the pulse wave exceeds the cardiovascular dynamic change threshold equivalent to the rate of change of the amplitude of the pulse wave of the peripheral blood vessel, and whether or not the rate of change of the dc component of the pulse wave exceeds the cardiovascular dynamic change threshold equivalent to the rate of change of the dc component of the peripheral blood vessel; and causing the control means to control the blood pressure measuring means and to measure blood pressure of a subject using the cuff if it is judged that the heart rate change exceeds the cardiovascular dynamic change threshold equivalent to the heart rate change, if it is judged that the rate of change of the amplitude of the pulse wave exceeds the cardiovascular dynamic change threshold equivalent to the rate of change of the amplitude of the pulse wave of the peripheral blood vessel, or if it is judged that the rate of change of the dc component of the pulse wave exceeds the cardiovascular dynamic change threshold equivalent to the rate of change of the dc component of the pulse wave of the peripheral blood vessel.
As described in the foregoing, the blood pressure monitoring apparatuses of the present invention are provided as not only judging whether or not the pulse wave propagation time change exceeds the preset pulse wave propagation time change threshold, but also judging whether or not the cardiovascular dynamic change, i.e., the heart rate change, the rate of change of the amplitude of the pulse wave at the peripheral blood vessel, or the rate of change of the dc component of the pulse wave at the peripheral blood vessel, exceed the preset cardiovascular dynamic change thresholds thereof and starting a blood pressure measurement for the subject if any one of the changes is judged to exceed the threshold thereof. There fore, the burden given to the subject in the past can be reduced. In addition, the blood pressure monitoring apparatuses of the present invention are also characterized as allowing a feeble blood pressure fluctuation that cannot be detected by the pulse wave propagation time change to be detected by the cardiovascular dynamic change. Therefore, a sudden turn for the worse in the blood pressure fluctuation of the subject can be monitored more reliably.